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Light as a massless object?

  1. Mar 8, 2007 #1
    Light is known a as some kind of energy that is being radiated; and energy is known as the fundamental source for any work. In addition, energy is known to be massless and so is light. Also light is the result of proton particles traveling in a very high speed known as the speed of light, which produce particular wavelengths which some are visible for our eyes.

    However, here comes the confusing part and my questions.

    First atoms are the most basic structures of any matter and element. Atoms consist of protons, electrons and neutrons. In addition, they can be weighted which means that they have mass. If light that consist of protons which contain mass; how can light be massless?

    Also there is the formula of gravity [G = (m1 * m2)/d2] which defines the gravitational force as a relationship between the mass of two objects and their distance. So, it is also said that light is influenced by gravity. If light has no mass, then how can it be influenced by the gravitational force?

    So which one is it? Is light a massless energy or a very small moving particles with mass?

    I have always though of it this way. Light probably is consisted of very small particles that rather of being some kind of energy; it has very high kinetic energy. Because the particles are so small and has so little mass, they are hardly influenced by gravity.

    For example, compare water liquid and water gas. Because water vapor has high kinetic energy and the mass is individually smaller than water liquid, they are less influenced by gravity and can easily escape the ground.

    To give it a step even further, i can think light as a state of matter that is followed after plasma. Just imagine any solid matter inside a sealed box. First we melt it into liquid. Then it becomes gas and ionizes into plasma. And suppose that the heat transmitted into the matter cannot escape the sealed box, the kinetic energy of each particle in the matter will increase making matter move into a higher speeds and the coalitions causes them to break apart into even smaller particles.

    A possible example from real life could be the atomic bomb. Because nuclear weapons are made of matter that decay faster than other stable elements, they can directly go from solid to light like the examples of solid to gas. So, while the amount of mass is the same, the amount of kinetic energy in each individual proton is really high and the coalition would be so hard that the momentum of each proton transfered to other objects would cause a chain of destructions.

    Although it is just my hypothesis, i would like to hear opinions. Please, correct me if i am wrong.

    Edit: I can't believe that a question of whether light is massless or not can end up with whether light can be considered as a physical state of matter or not.
    Last edited: Mar 8, 2007
  2. jcsd
  3. Mar 8, 2007 #2


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    proton particles travelling? were you meant to say "photons"?

    by the way, you can further chop protons and neutrons down to a thing called "quarks", while electrons are indeed elementary.

    errr... a completely confusing and wrong statement

    judging by the way you have said this, it appears that you are trying to use Newtonian Gravity to explain effects (such as massive objects bending light) which come from Einstein's theory of gravity. So let's not confuse the two. In Einstein's version of gravity, objects move in the way they do (under the influence of other massive objects) because massive objects distort the shape of spacetime around themselves hence changing the path of the surrounding objects. These objects include light/photons.

    light is massless, a form of energy and moves at the "speed of light"

    nice try but not quite right :smile:

    do not mix matter/stuff with light/energy.
    you may think of light as packets of energy ---photons, but shouldn't go as far as imagining that they are indeed "particles" in the normal sense.

    The universe as we know it (so far) is made up of two types of things (treating spacetime as just a background where everything lives in):

    - "matter" particles
    - "interaction" particles

    "matter" particles are the elementary particles that make up atoms. And there are two types of these called quarks and leptons (eg. electron is a lepton). Protons, neutrons are made up of three quarks of different flavors.

    "interaction" particles are the "messengers"... you may ask if I put a +ve charge next to another +ve charge how does the second one knows the presence of the first and repel? Well, this information is carried by these "interaction" particles (these are virtual, in this case). We sometimes take "action at a distance" for granted but if you think about it, it seems quite clear that unless two things can somehow communicate there is no way they can "interact"
    by the way, a virtual photon play the role of the messenger in the above electromagnetic example.

    but light is form of energy alright.....and a photon is massless.... that's fine too.
  4. Mar 8, 2007 #3


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    Did you just confused "photons" with "protons"?

    I would also like to suggest that since you are new here, that you spend some time browsing the various physics forums first. Your question has been addressed in one way or another in various threads in the Quantum Physics and Special/General Relativity forums.

    Last edited: Mar 8, 2007
  5. Mar 8, 2007 #4
    Edit: lol, I see. I confused Protons with Photons. There are so similar. Thanks.
    Last edited: Mar 8, 2007
  6. Mar 8, 2007 #5
    They may be similar words, but they are very different entities!
  7. Mar 8, 2007 #6
    Yeah, i am glad i am being corrected. :biggrin:
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